While the Constitution grantsCongress the sole power to formally declare war, almost every modern president has initiated military action using their authority as Commander-in-Chief.

The U.S. has not issued a formal declaration of war since World War II. Here are the notable presidents who have bypassed prior congressional consultation or formal declarations for major conflicts:
The Post-WWII "Undeclared War" Era

Harry S. Truman: Committed U.S. forces to the Korean War (1950) by labeling it a "police action" under a UN Security Council resolution, completely bypassing Congress.
Lyndon B. Johnson: Dramatically escalated the Vietnam War after the 1964 Gulf of Tonkin incident. While he had a resolution, critics argue he misled Congress to gain broad authority without a formal war declaration.
Richard Nixon: Expanded the Vietnam War by ordering the secret bombing of Cambodia in 1970 without notifying or consulting Congress.
Bill Clinton: Launched a 78-day NATO bombing campaign in Kosovo (1999) without congressional authorization, continuing even after the House of Representatives voted against it.
Barack Obama: Initiated military intervention in Libya (2011) to oust Muammar Qaddafi, arguing it did not constitute "hostilities" under the War Powers Resolution.
Donald Trump: Ordered airstrikes in Syria (2017, 2018) and, most recently in early 2026, initiated significant strikes against Iran without seeking a prior vote or consultation from Congress.

Historical Precedents

John Adams: Engaged in the Quasi-War with France (1798–1800) without a formal declaration.
Abraham Lincoln: At the start of the Civil War (1861), he acted while Congress was in recess to raise an army and blockade Southern ports.
Ronald Reagan: Ordered the invasion of Grenada (1983) and the bombing of Libya (1986) unilaterally.
George H.W. Bush: Ordered the invasion of Panama (1989) and deployed troops to Somalia (1992) as executive actions.

Since the War Powers Resolution of 1973, presidents are supposed to report to Congress within 48 hours, but many have utilized the Commander-in-Chief clause to act first and explain later.

Declaring war through Congress may be in the constitution but in practice it really isn’t done anymore.

Warfare has changed since the 1700s. It isn’t country against country so much anymore.

Now it’s factional against faction.

But Congress needs to rein this in. I understand a lot of people want the president to react within minutes to a crisis which is why Congress has given up most of its power, but in this day and age that is kind of absurd. If there was an attack on America, using web meetings, there is no reason a quorum of both houses of Congress could not be online within minutes and have a method in place granting the president military authorization to deal with the problem


As for preemptive attacks where we are the hostile nation and its planned way ahead of time, that should always go through Congress.